1. Field of the Invention
The present invention relates to a thermal shield device provided in a crystal-pulling apparatus for pulling and growing a silicon monocrystal ingot from a melt and (hereinafter also referred to as a crystal-pulling apparatus) also relates a crystal-pulling apparatus using such a thermal shield device.
2. Description of Related Art
Heretofore, various apparatuses for pulling and growing silicon monocrystal ingots have been disclosed in many publications. Among them, for example, Examined Japanese Patent Application No. 57-40119 (1982) discloses a crystal-pulling apparatus comprising a chamber having a quartz crucible that reserves a silicon melt and a thermal shield device provided between an external surface of silicon monocrystal ingot and an internal surface of the quartz crucible so that the ingot is enclosed with the thermal shield device. That is, the thermal shield device comprises a tubular member that surrounds the periphery of the silicon monocrystal ingot to be pulled upward and is positioned above the surface of the silicon melt with the predetermined space between them to prevent the radiation of heat from a heater. A liquid level of the silicon melt is gradually decreased as the silicon crystal is gradually pulled from the silicon melt, so that an inner peripheral wall of the quartz crucible becomes being exposed. The radiation of heat from the inner peripheral surface of the exposed quartz crucible is emitted toward the outer peripheral surface of the silicon monocrystal ingot. Thus, the thermal sealed member blocks such radiation to prevent that the radiation of heat extends to the outer peripheral surface of the silicon monocrystal ingot, so that the silicon monocrystal ingot can be cooled quickly to accelerate a solidification thereof during the pulling step.
In addition, Unexamined Japanese Patent Application No. 8-325090 (1996) discloses a tubular member of such a kind of the thermal shield device, which is configured as a multi-layer structure comprising a base material and a covering member. The base material is a graphite or the like having a heat-resisting property at a temperature corresponding to that of the radiation. On the other hand, the covering member is made of a quartz or the like having a lower thermal emissivity in comparison with that of the base material. Such a configuration of the thermal shield device increases the effects of preventing the radiation of heat from the crucible and the heater to the silicon monocrystal ingot by covering the base material having a high thermal emissivity with the covering member having a thermal emissivity lower than that of the base material. Consequently, the rate of pulling the silicon monocrystal ingot from the melt can be increased as the cooling of the silicon monocrystal ingot is accelerated, so that the productivity of the silicon monocrystal ingot can be increased.
However, the thermal shield device of the crystal-pulling apparatus disclosed in Unexamined Japanese Patent Application No. 8-325090 (1996) causes the nonuniform distribution of temperature in a portion of the silicon monocrystal ingot in proximity to the silicon melt. That is, the maximum temperature can be observed in the center of such a portion, while the temperature is gradually decreased from the center to the outside and a sudden decrease in temperature is observed on the outer periphery of that portion. It is conceivable that the temperature deference between the center and the outer periphery of the silicon monocrystal ingot may be further increased as a diameter of the silicon monocrystal ingot is further increased. Therefore, there is a possibility that a thermal stress may be generated in the silicon monocrystal ingot as a result of the above-described temperature difference.
It is an object of the present invention to provide a thermal shield device to be provided in a crystal-pulling apparatus for pulling and growing a silicon crystal from a melt to obtain a silicon monocrystal ingot. The thermal shield device allows the prevention of the steep decrease in temperature of the outer periphery of a silicon monocrystal ingot being pulled from the silicon melt to inhibit the generation of thermal stress in the silicon monocrystal ingot.
It is another object of the present invention to provide a crystal-pulling apparatus for pulling and growing a silicon crystal from a melt to obtain a silicon monocrystal ingot. The apparatus has a thermal shield device that allows the prevention of the steep decrease in temperature of the outer periphery of a silicon monocrystal ingot being pulled from the silicon melt to inhibit the generation of thermal stress in the silicon monocrystal ingot.
In the first aspect of the present invention, a thermal shield device equipped in a crystal-pulling apparatus for pulling a silicon monocrystal ingot from a silicon melt reserved in a quartz crucible having an outer peripheral surface encircled with a heater, comprises: a tubular part to be used for surrounding a silicon monocrystal ingot being pulled and grown in an upward direction to prevent radiant heat from the heater toward the silicon monocrystal ingot, having a lower end positioned above a surface of the silicon melt with a predetermined spacing therebetween; and a protruding part formed on a lower portion of the tubular part and filled with a thermal-insulating member, which protrudes in an inward direction and has a bottom wall facing to the silicon melt.
Here, the bottom wall may be shaped like a ring having an outer edge connected to a lower edge of the tubular part and may extend horizontally to the proximity of an outer peripheral surface of the silicon monocrystal ingot. The protruding part may further include: a vertical wall positioned at a predetermined distance from the outer peripheral surface of the silicon monocrystal ingot and connected to an inner edge of the bottom wall, extending in parallel to an axis of the silicon monocrystal ingot or extending at an angle of xe2x88x9230 to +30 degrees with respect to the axis of the silicon monocrystal ingot; and a cone-shaped top wall having a lower edge connected to an upper edge of the vertical wall and an upper edge attached to an inner peripheral surface of the tubular part, extending in an upward direction with a gradual increase in diameter.
Here, an inclined inner wall extending in an upward direction with a gradual decrease in diameter may be formed as an intersection between the vertical wall and the bottom wall and inclined at an angle of 80 degrees or less but not zero with respect to an under surface of the bottom wall so as to satisfy that the relationship between the diameter xe2x80x9cdxe2x80x9d of the silicon monocrystal ingot and the vertical distance L1 from the lower edge of the vertical wall to the under surface of the bottom wall is represented as 0xe2x89xa6L1xe2x89xa6d/2.
Here, the height xe2x80x9cHxe2x80x9d of the vertical wall may be in the range of 10 mm to d/2 where xe2x80x9cdxe2x80x9d denotes the diameter of the silicon monocrystal ingot.
Here, the spacing between the outer peripheral surface of the silicon monocrystal ingot and the vertical wall may be in the range of 10 mm to 30 mm.
Here, the relationship among the diameter xe2x80x9cD1xe2x80x9d of the lower edge of the tubular part, the inner diameter xe2x80x9cD2xe2x80x9d of the quartz crucible, and the diameter xe2x80x9cdxe2x80x9d of the silicon monocrystal ingot may be represented as 1.65d less than D1 less than D2.
Here, the tubular part may be formed with a gradual decrease in diameter in a downward direction.
Here, the tubular part may include an inner tubular part, an outer tubular part, and a thermal-insulating member filled in the space between the inner tubular part and the outer tubular part.
Here, at least one ring-shaped heat transfer member having an outer peripheral edge connected to the tubular part or the inclined outer wall and an inner peripheral edge connected to the vertical wall or the inclined inner wall, may be transversely formed in the inside of the protruding part.
Here, an inclined outer wall extending in a downward direction with a gradual decrease in diameter may be formed as an intersection between the tubular part and the bottom wall and inclined at an angle of 80 degrees or less but not zero with respect to an under surface of the bottom wall so as to satisfy that the relationship between the diameter xe2x80x9cdxe2x80x9d of the silicon monocrystal ingot and the vertical distance xe2x80x9cL2xe2x80x9d from the lower edge of the tubular part to the under surface of the bottom wall is represented as 0xe2x89xa6L2xe2x89xa6d/2.
Here, the bottom wall may be shaped like a cone having an outer edge connected to a lower edge of the tubular part and extends to the proximity of an outer peripheral surface of the silicon monocrystal ingot, with a gradual decrease in diameter in an upward or downward direction at an angle of 80 degrees or less but not zero with respect to a horizontal plane. The protruding part may further include: a vertical wall positioned at a predetermined distance from the outer peripheral surface of the silicon monocrystal ingot and connected to an inner edge of the bottom wall, extending in parallel to an axis of the silicon monocrystal ingot or extending at an angle of xe2x88x9230 to +30 degrees with respect to the axis of the silicon monocrystal ingot; and a cone-shaped top wall having a lower edge connected to an upper edge of the vertical wall and an upper edge attached to an inner peripheral surface of the tubular part, extending in an upward direction with a gradual increase in diameter.
Here, the height xe2x80x9cHxe2x80x9d of the vertical wall may be in the range of 10 mm to d/2 where xe2x80x9cdxe2x80x9d is the diameter of the silicon monocrystal ingot.
Here, the spacing between the outer peripheral surface of the silicon monocrystal ingot and the vertical wall may be in the range of 10 mm to 30 mm.
Here, the relationship among the diameter xe2x80x9cD1xe2x80x9d of the lower edge of the tubular part, the inner diameter xe2x80x9cD2xe2x80x9d of the quartz crucible, and the diameter xe2x80x9cdxe2x80x9d of the silicon monocrystal ingot may be represented as 1.65d less than D1 less than D2.
Here, the tubular part may be formed with a gradual decrease in diameter in a downward direction.
Here, the tubular part may include an inner tubular part, an outer tubular part, and a thermal-insulating member filled in the space between the inner tubular part and the outer tubular part.
Here, at least one ring-shaped heat transfer member having an outer peripheral edge connected to the tubular part or the inclined outer wall and an inner peripheral edge connected to the vertical wall or the inclined inner wall, may be transversely formed in the inside of the protruding part.
Here, the bottom wall may include: an outer bottom wall having an outer edge connected to a lower edge of the tubular part, which is inclined at an angle of 80 degrees or less but not zero with respect to a horizontal plane, with gradual decrease in diameter in a downward direction; and an inner bottom wall having an outer edge connected to a lower edge of the outer bottom wall and an inner edge extending to the proximity of the outer peripheral surface of the silicon monocrystal ingot, which is inclined at an angle of 80 degrees or less but not zero with respect to a horizontal plane, with a gradual decrease in diameter in an upward direction. The protruding part may further include: a vertical wall positioned at a predetermined distance from the outer peripheral surface of the silicon monocrystal ingot and connected to an inner edge of the bottom wall, which extends in parallel to an axis of the silicon monocrystal ingot or extending at an angle of xe2x88x9230 to +30 degrees with respect to the axis of the silicon monocrystal ingot; and a cone-shaped top wall having a lower edge connected to an upper edge of the vertical wall and an upper edge attached to an inner peripheral surface of the tubular part, extending in an upward direction with a gradual increase in diameter.
Here, the height xe2x80x9cHxe2x80x9d of the vertical wall may be in the range of 10 mm to d/2 where xe2x80x9cdxe2x80x9d may be the diameter of the silicon monocrystal ingot.
Here, the spacing between the outer peripheral surface of the silicon monocrystal ingot and the vertical wall may be in the range of 10 mm to 30 mm.
Here, the relationship among the diameter xe2x80x9cD1xe2x80x9d of the lower edge of the tubular part, the inner diameter xe2x80x9cD2xe2x80x9d of the quartz crucible, and the diameter xe2x80x9cdxe2x80x9d of the silicon monocrystal ingot may be represented as 1.65d less than D1 less than D2.
Here, the tubular part may be formed with a gradual decrease in diameter in a downward direction.
Here, the tubular part may include an inner tubular part, an outer tubular part, and a thermal-insulating member filled in the space between the inner tubular part and the outer tubular part.
Here, at least one ring-shaped heat transfer member having an outer peripheral edge connected to the tubular part or the inclined outer wall and an inner peripheral edge connected to the vertical wall or the inclined inner wall, is transversely formed in the inside of the protruding part.
In the second aspect of the present invention, a crystal-pulling apparatus for pulling and growing a silicon monocrystal ingot from a silicon melt, reserved in a quartz crucible having an outer peripheral surface encircled with a heater, comprising a thermal shield device that includes: a tubular part to be used for surrounding a silicon monocrystal ingot being pulled and grown in an upward direction to prevent radiant heat from the heater toward the silicon monocrystal ingot, having a lower end positioned above a surface of the silicon melt with a predetermined spacing therebetween; and a protruding part formed on a lower portion of the tubular part and filled with a thermal-insulating member, which protrudes in an inward direction and has a bottom wall facing to the silicon melt.
Accordingly, the present invention is able to solve the problems that in the conventional thermal shield device the nonuniform distribution of temperature in a portion of the silicon monocrystal ingot in proximity to the silicon melt where the maximum temperature is observed in the center of such a portion while the temperature is gradually decreased from the center to the outside and a sudden decrease in temperature is observed on the outer periphery of that portion. According to the present invention, on the other hand, the heat radiation from the outer peripheral surface of the silicon monocrystal ingot can be reflected by the vertical wall of the protruding part or prevented by the temperature of the protruding part which is considerably increased by the heat radiation from the high-temperature silicon melt. Thus, the protruding part prevents the steep decrease in temperatures of the outer peripheral portion of the silicon monocrystal ingot. Consequently, the distribution of temperature from the center to the outer peripheral portion of such an ingot can be substantially uniformed. That is, the protruding part allows a vertical thermal gradient in the silicon monocrystal ingot where the radial distribution of temperature in any part thereof is substantially uniform. Thus, the slip generation and first dislocation generation in the resulting product can be prevented as a result of the prevention of thermal stress to be applied in the silicon monocrystal ingot.
According to the present invention, furthermore, the cone-shaped top allows that an inert gas downwardly passing through the space between the outer peripheral portion of the silicon monocrystal ingot and the outer peripheral surface of the tubular part can be smoothly introduced into the space between the silicon melt and the protruding part. Thus, the thermal-insulating part effectively prevents the decrease in temperature of the outer peripheral portion of the silicon monocrystal ingot by accumulating radiant heat from the silicon melt to the protruding part.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.